engleski

Zooming into Lowe syndrome: the role of OCRL in platelets

Lowe syndrome (LS) is a rare, X-linked disorder that affects the brain, the eyes, and the kidneys. It is caused by mutations in the oculocerebrorenal syndrome of Lowe (OCRL) protein, a 5-phosphatase that dephosphorylates phosphatidylinositol-4, 5- bisphosphate [PI(4, 5)P2] resulting in the formation of phosphatidylinositol-4-monophosphate (PI4P). The most important roles of PI(4, 5)P2 are the regulation of endocytosis and actin reorganization. Besides the before mentioned symptoms, it has been shown that LS patients have problems with bleedings suggesting platelet (PLT) dysfunction. PLTs are the smallest blood cells that circulate in the blood in their resting state. When they encounter vessel wall damage, they activate and aggregate forming a clot and stopping the bleeding. The activation of PLTs requires shape change which led us to hypothesize that OCRL could have an important role in actin reorganization. Here we show that pharmacological inhibition of OCRL in PLTs spread on fibrinogen leads to impaired PLT activation with excessive formation of actin nodules. These actin nodules partially and extensively colocalize with SNX9 and vinculin or ARP2/3 complex and phosphotyrosine, respectively. These data suggest impaired cytoskeletal rearrangement ; however, by flow cytometry analysis we show that the net change of actin polymerization is not affected. The examination of signalling pathways in thrombin or TRAP-6 activated PLTs by Western blot revealed that OCRL inhibited PLTs have decreased myosin light chain (MLC) phosphorylation, with no difference in p-p38 or p-ERK. Moreover, the flow cytometry analysis of P-selectin surface expression or αIIbβIII integrin conformation change in TRAP-6 activated PLTs showed that the inhibition of OCRL does not affect PLT granule release or integrin activation. Our data suggest that OCRL controls actin reorganization, but not degranulation or integrin activation which could explain mild bleeding disorders in LS patients.

OCRL, PI(4, 5)P2, platelets, Lowe syndrome

nije evidentirano